1. Field of the Invention
The present invention relates to an ink jet recording head for discharging ink to perform recording, and a recording apparatus provided with this recording head.
2. Related Background Art
A recording apparatus that includes an ink jet recording head on the basis of supplied recording information prints images on a recording medium (a recording material), such as paper, a plastic sheet or an OHP (Overhead Projector) sheet. In the specifications for the present invention, “images” are expressions used not only for things such as characters, symbols and drawings that provide individual definitions, but also for things such as patterns and full colors that provide no definitions. “Recording” and “image forming” represent general operations for forming these images.
The ink jet recording apparatus heats or vibrates ink supplied to ink jet recording head, and discharges the ink toward a recording medium, such as a recording sheet, to perform image recording. Ink droplets, discharged by the ink jet recording head and attached to the recording medium, are spread on the recording medium, and form dots. Then, on the recording medium, an image is form as a set of dots. The area covered by a single dot is greatly dependant on the size of ink droplet, i.e., on the volumeof the ink discharged. Therefore, controlling the volume (amount) of ink discharge is very important to the process of forming high-resolution images using the ink jet method.
The volume of the ink discharged is acutely affected by the temperature of the ink and the temperature at the recording head, and varies as these temperatures change. Therefore, management of the temperature at the ink jet recording head and the temperature of the ink are vitally important, especially in a low temperature environment wherein the viscosity of the ink is increased and viscous resistance (drag) in the ink discharge nozzles (hereinafter referred to as “nozzles”) of the ink jet recording head is increased, which drastically reduces the volume of ink that is discharged.
Therefore, a structure wherein a heat generation device (hereinafter referred to as a “temperature adjustment heater” or a “sub heater”), for heat insulation, is provided inside an ink jet recording head is disclosed in Japanese Patent Laid-Open Publication No. Hei 7-52387. According to the ink jet recording head disclosed in this publication, a sub heater is driven in a low temperature environment and raises the temperatures both of the ink and at the ink jet recording head, so as to stabilize the volume of ink discharged.
Recently, in order to provide high-quality recording, such as is required for printing photographs, using an ink jet recording apparatus, the trend is to minimize, to the extent possible, the sizes of the ink droplets that are discharged by an ink jet recording head. For such an ink jet recording head, which discharges minute droplets, since the openings of the discharge ports at their nozzle ends tend to be reduced, and viscous drag in the nozzles tends to be increased, the volume of ink discharged is sharply reduced within a short period of time, especially when the temperature is decreased. In order to provide the above-described heat insulation control at a high response speed and to stabilize the volume of the ink discharged, the provision of multiple sub heaters is effective. However, according to this method, the area of a substrate on which the sub heaters are mounted would be increased, and accordingly, the size of the entire ink jet recording head would be greater. Further, the manufacturing costs would rise.